Non-Contact Voltage Detector

Introduction: Non-Contact Voltage Detector

Non-contact voltage detector is a handy device which is useful for indicating if there current running in the circuit or system.

it consist of three transistors which acts as a switch in the circuit which amplify the current detected and a parallel connection of resistor in a increasing manner from 220ohm to 1Mohm which minimize the current passing through in the circuit and minimizes the chance of a busted battery.

The first voltage detector was used to indicate electricity passing through the AC lines, power line, and telephone lines in order to communicate if this line is busted or damage.

Step 3: A Brief Info About Transistors

A transistor is an electrical component that functions, most basically, as a switch — in principle not so different from a light switch. Instead of a physical movement, however, a transistor is controlled by a flow of electricity. And unlike your basic light switch, a transistor can be on, off, or somewhere in between.

Most transistors have three connections: one for current in, one for current out, and one that controls the “switch.” The current flowing through a transistor can be larger than the current controlling it, so it can become an amplifier: Connect the input to a power source (like a battery), and the control lead to a weak signal (like a guitar pickup), and the output will sound like the control signal, only louder. Just how much louder depends on a lot of things, but a factor of 200 is routine. This number is called gain.

If you use the output from one transistor to control another, the gains multiply. With two transistors, the ideal gain becomes 200 × 200 = 40,000, and with three transistors (as in this circuit), 200 × 200 × 200 = 8,000,000! That huge gain lets you use it to detect the tiniest movements of electricity — even those created at a distance by induction or static charge!

Step 6: The Usage.

Warning: Experiment and have fun but never ever touch the copper strip to a bare wire that has live voltage!

Hold the non-contact voltage detector near a live AC power line and depress the button: it will light up.

The detector can be a little sensitive about the position it's held in so if the LED doesn't light up, try moving the detector around a little, while keeping the copper strip close to the wire.It's also fun to see how it detects static electricity. Try quickly rubbing your hand across some carpet several times then hold your hand near the copper strip. The LED should light up brightly from the static charge build up.